Tetranuclear [Cu 3 Ln] complexes derived from a tetraketone-type ligand.

A series of tetranuclear [Cu 3 Ln] complexes, [Cu 3 Gd(L) 3 (NO 3 ) 2 (H 2 O) 3 ](NO 3 )·H 2 O (1), [Cu 3 Tb(L) 3 (NO 3 ) 2 (H 2 O) 3 ](NO 3 ) (2) and [Cu 3 Dy(L) 3 (NO 3 ) 3 (H 2 O) 2 ]·1.5(H 2 O) (3), were synthesized by a one-pot reaction using a simple tetraketone-type ligand (H 2 L = (3 Z ,5 Z )-4,5-dihydroxy-3,5-octadiene-2,7-dione). X-ray structural analyses revealed that each complex has a planar tetranuclear core of [Cu 3 Ln] (Ln = Gd, Tb, and Dy), in which the Ln ion is accommodated in the centre of a Cu 3 O 6 metallocycle. A cryomagnetic study revealed that all complexes show intramolecular ferromagnetic interactions between Cu(II) and Ln(III) ions. The [Cu 3 Gd] complex (1) has an S T = 5 spin ground state and shows a magneto-caloric effect with a maximum magnetic entropy change (-Δ S m ) of 16.4 J kg -1 K -1 (5 T, 2.4 K). On the other hand, the [Cu 3 Tb] complex (2) shows a slow magnetic relaxation behavior under a zero magnetic field. The analysis of an Arrhenius plot reveals that the effective energy barrier of spin reversal is 13.1 K. The [Cu 3 Dy] complex (3) also shows a slow magnetic relaxation under 1300 Oe dc magnetic field with an effective energy barrier of 6.82 K.